With the aim of proving an antibacterial composition against oral bacteria and the like capable of inducing Th1 cell proliferation or activation in an intestinal tract, the present inventors have found out that bacteria that suppress colonization and the like of the oral bacteria and the like in the intestinal tract are present in an intestinal microbiota. Moreover, the present inventors have succeeded in isolating intestinal bacteria that suppress intestinal colonization and the like of oral bacteria and the like.